Recently, as portable electronic instruments, such as portable computers, portable phones and camcorders, have been steadily developed so that they are downsized and lightened, lithium secondary batteries used as drive sources for the electronic instruments are also required to have a compact size and a light weight.
A lithium secondary battery includes a cathode, an anode and an electrolyte. Upon the first charge cycle, lithium ions are deintercalated from a cathode active material. Then, the lithium ions are intercalated into an anode active material such as carbon particles, and are deintercalated from the anode active material upon discharge. In this manner, lithium ions transfer energy while they reciprocate between the cathode and the anode, thereby allowing the battery to be charged/discharged. However, performance of a lithium secondary battery may be degraded by the deterioration of an anode during repeated charge/discharge cycles. Also, when a battery is exposed to high temperature conditions, safety of the battery may be degraded by the gas generation in the battery.
To solve the aforementioned problems, EU 683537 and JP 1996-45545 suggest a method for minimizing deterioration of an anode by using vinylene carbonate (referred to also as VC hereinafter) that forms a passivation layer on a carbon anode. Additionally, JP 1999-162511, JP 1999-339850 and JP 2004-47131 disclose the fact that propane sultone (referred to also as PS hereinafter) and a propane sultone-based compound can improve the long-term safety and lifespan characteristics of a battery.